1. The Field of the Invention
The present invention relates to orthodontic brackets, more particularly to self-ligating orthodontic brackets that include a bracket base, at least one slot or other feature for receiving an arch wire, and a ligation cover.
2. The Relevant Technology
Orthodontics is a specialized field of dentistry that involves the application of mechanical forces to urge poorly positioned, or crooked, teeth into correct alignment and orientation. Orthodontic procedures can be used for cosmetic enhancement of teeth, as well as medically necessary movement of teeth to correct underbites or overbites (xe2x80x9cbuck teethxe2x80x9d). Orthodontic treatment can improve the patient""s occlusion, or enhanced spatial matching of corresponding teeth.
The most common form of orthodontic treatment involves the use of orthodontic brackets and wires, which together are commonly referred to as xe2x80x9cbracesxe2x80x9d. Orthodontic brackets, more particularly the bracket bases, are small slotted bodies configured for direct attachment to the front (or xe2x80x9clabialxe2x80x9d) surfaces of the patient""s anterior, cuspid, and bicuspid teeth or, alternatively, for attachment to bands which are, in turn, cemented or otherwise secured around the teeth. Once the brackets are affixed to the patient""s teeth, such as by means of glue or cement, a curved arch wire is inserted into the slot of each bracket. The arch wire acts as a template or track to guide movement of the teeth into proper alignment. End sections of the arch wire are typically captured within tiny appliances known as xe2x80x9cbuccal tubesxe2x80x9d affixed to the patient""s molars.
There are two distinct classes of orthodontic brackets: those that require the use of ligatures to fasten the arch wire to the bracket, and those that are self-ligating. Before the emergence of self-ligating brackets, small ligature wires or elastomeric bands were necessary to hold the arch wire in a securely seated position in the brackets. Ligatures or some other form of fastening means are essential to ensure that the tensioned arch wire is properly positioned around the dental arch, and to prevent the wire from being dislodged from the bracket slots during chewing of food, brushing of teeth, or application of other forces. One type of commercially available ligature is a small, elastomeric O-ring, which is installed by stretching the O-ring around small wings known as xe2x80x9ctie wingsxe2x80x9d that are connected to the bracket body. Metal ligatures may also be used to retain arch wires within the bracket slots.
In an effort to simplify the process of installing braces, various self-ligating brackets have been developed. The term xe2x80x9cself-ligating bracketxe2x80x9d refers to a class of orthodontic brackets that include some sort of ligation cover or clasp which encloses or otherwise retains the arch wire within the slot of the base. There are both xe2x80x9cpassivexe2x80x9d and xe2x80x9cactivexe2x80x9d self-ligating orthodontic brackets. The term xe2x80x9cpassivexe2x80x9d bracket refers to brackets that only loosely retain the arch wire therein, such that considerable movement between the arch wire and bracket base is possible. The term xe2x80x9cactivexe2x80x9d bracket refers to brackets in which the self-ligating arch wire cover exerts force onto the arch wire, resulting in more precise and controlled tooth movement.
The first self-ligating bracket, known as the Russell bracket, was developed by Dr. Jacob Stolzenberg in the early 1930s. This bracket, which uses a set screw to ligate the arch wire within a slot of a threaded base, was revolutionary but perhaps ahead of its time because the concept of self-ligating brackets fell more or less into obscurity until the early 1970s.
In 1971, Dr. Jim Wildman of Eugene, Oregon developed the EDGELOK bracket, which has a round body with a rigid labial sliding cap. A special opening tool is used to move the slide occlusally for arch wire insertion. When the cap is closed over the arch wire with finger pressure, the bracket slot is converted to a tube. The EDGELOK bracket was the first xe2x80x9cpassivexe2x80x9d self-ligating bracket. That is, the bracket, while retaining the arch wire therein, does not exert pressure onto the wire. Instead, the arch wire is free to slide relative to the bracket. The EDGELOK bracket is describe in U.S. Pat. Nos. 3,748,740 and 3,854,207 to Wildman. Other patents to Dr. Wildman include U.S. Pat. Nos. 5,094,614, 5,474,446 and 5,863,199. In 1998, Dr. Wildman introduced the TWIN-LOCK bracket, which includes a flat, rectangular slide, housed between the tie wings of an edgewise twin bracket.
A similar bracket to the EDGELOK bracket, called the MOBIL-LOCK bracket, was developed by Dr. Franz Sander of Ulm, Germany, which requires a special tool to rotate the semicircular labial disk into the open or closed position.
Between 1976 and 1980, Dr. Herbert Hanson of Hamilton, Ontario, Canada developed the SPEED bracket, which features a curved spring clip that wraps occluso-gingivally around a miniaturized bracket body. The clip is moved occlusally using special tools to permit arch wire placement, then seated gingivally using finger pressure. The clip constrains and interacts with the arch wire to some degree such that the SPEED bracket was the first xe2x80x9cactivexe2x80x9d bracket system.
In 1986, Dr. Erwin Pletcher developed the ACTIVA bracket, which has an inflexible, curved arm that rotates occluso-gingivally around a cylindrical bracket body (see U.S. Pat. Nos. 4,077,126, 4,371,337, 4,419,078, 4,522,490, 4,559,012 and 5,322,435 to Pletcher). The arm can be opened and closed using finger pressure.
In 1995, Dr. Wolfgang Heiser of Innsbrxc3xcck, Austria developed the TIME bracket, which is similar in appearance to the SPEED bracket, and which features a rigid, curved arm that wraps occluso-gingivally around the labial aspect of the bracket body. A special instrument is used to pivot the arm either gingivally into the slot-open position, or occlusally into the slot-closed position. The stiffness of the bracket arm prevents any substantial interaction with the arch wire, thereby making the TIME bracket a passive bracket.
Dr. Dwight Damon of Spokane, Wash. developed the Damon SL I and the Damon SL II brackets in 1996 and 1999, respectively (see U.S. Pat. No. 6,071,118 to Damon). Both are edgewise twin brackets. The difference between the two is that the first features a labial cover that straddled the tie wings, while the second incorporates a flat, rectangular slide between the tie wings. In both versions, the slide moves incisally on the maxillary brackets and gingivally on the mandibular brackets. Special opening and closing pliers are required to move the slide.
There are many other variations and adaptations of the foregoing self-ligating brackets that have been developed by others. See, e.g., U.S. Pat. No. 4,786,252 to Fujita, U.S. Pat. No. 4,712,999 to Rosenberg, U.S. Pat. No. 4,492,573 to Hanson, U.S. Pat. No. 4,103,423 to Kessel, and U.S. Pat. No. 6,071,119 to Christoffet al.
In general, conventional self-ligating brackets are complicated in design, complex to assemble, and difficult to use in practice. Conventional orthodontic brackets often require many trips to the orthodontist for periodic readjustment and maintenance. Therefore, there has been a long-felt need to find new designs and materials that can simplify the manufacture of orthodontic brackets, as well as the installation and subsequent maintenance of such brackets. In particular, there is a need for orthodontic brackets that are easy to open and close, that provide active ligation without the need for special tools to open and close the arch wire restraining means, which are easily manufactured and installed by the orthodontist, which provide greater versatility together, and which are of simplified design.
For example, it would be an improvement in the art to provide one-piece, self-ligating orthodontic brackets that can be manufactured in a single molding step. It would be a further improvement to provide self-ligating brackets that include a plurality of plastic materials from which the base and cover can be made so as to maximize the beneficial properties of each plastic material. It would be an additional improvement to provide orthodontic brackets with special hinge and locking features between the ligation cover and bracket base or increased safety and ease of use. It would be an improvement to provide orthodontic brackets capable of dynamic active ligation of an arch wire as the tooth is realigned so as to reduce or eliminate the need for subsequent adjustments. It would yet be an improvement to provide orthodontic brackets having two or more initially open arch wire slots that can be ligated by a single ligation cover. It would also be an improvement to provide a ligation cover that was biased so as to preferentially remain in an open and/or closed position.
Orthodontic brackets that incorporate one or more of the these and other improvements are disclosed and claimed herein.
The orthodontic brackets according to the present invention encompass one or more of the improvements and features disclosed herein, which result in a generally low-cost bracket that is simple to manufacture, compact in construction, and easy to install and adjust. In general, the orthodontic brackets according to the invention will include at least one of the following improved features:
1. a ligation cover that includes a film hinge, which is a localized area of reduced cross-sectional thickness, about which at least a portion of the ligation cover can rotate so as to open and close relative to the bracket base;
2. a spring element extending from an underside of the ligation cover and that is able to absorb mechanical energy from an arch wire and then release such energy over time to provide continuous active ligation of the arch wire;
3. a general spring feature associated with, or incorporated into, the ligation cover that is able to absorb mechanical energy from the arch wire and then release such energy over time in order to provide dynamic active ligation of an arch wire associated with a bracket base;
4. an orthodontic bracket that includes a deformable or flexible ligation cover that facilitates locking and unlocking of the cover relative to a bracket base that includes a lip, overhang or other structure within which the ligation cover can be slideably inserted or withdrawn;
5. a spring element interconnecting the ligation cover and bracket base that urges the ligation cover to remain open while in an open position and/or to remain closed while in a closed position relative to the bracket base;
6. a ligation cover that is biased toward remaining open when in an open position and toward remaining closed while in a closed position, such that positive pressure or force is required to selectively open and close the cover each time, and such that the cover is optionally able to apply a ligation force onto an arch wire associated with the bracket even when the ligation cover is not securely locked to the bracket base;
7. an orthodontic bracket that is manufactured using two-color molding of different types of plastic materials, such as a harder, more durable plastic for the bracket base and a more flexible and resilient plastic for the ligation cover;
8. an orthodontic bracket that includes at least two initially open arch wire slots configured to accept or receive two or more separate arch wires that can be at least partially occluded by a single ligation cover in a single action of locking or closing the ligation cover relative to the bracket base so as to ligate the arch wires; or
9. an orthodontic bracket having a safety locking feature that provides enhanced locking of the ligation cover to the bracket in response to increased pressure by an arch wire bearing upwardly against a ligation cover.
In general, depending on which of the foregoing features are incorporated into a particular orthodontic bracket, the orthodontic bracket may provide either passive or active ligation of an arch wire associated with the bracket base. The bracket may include a bracket base and ligation cover may be molded as a single, unitary piece, or else formed separately and then joined together. The ligation cover may or may not include specific hinge structures or regions, but may instead bend or flex along a substantial length of the ligation cover. An orthodontic bracket may be manufactured from a single plastic or metal material, or from multiple materials, such as metal and plastic or two or more plastics. The ligation cover may be flexible or rigid. The bracket base may include a single arch wire slot or it may include multiple arch wire slots. In some cases, the ligation cover will be designed to cover a single arch wire slot and in others, it may ligate two or more open slots. In some cases, one or more slots may be provided that are not ligated by the ligation cover such that conventional ligatures may be required to ligate additional arch wires disposed therein. Unless otherwise specified or restricted, any feature known in the art of orthodontic brackets, bases and ligation covers may be used in conjunction with a particular orthodontic bracket that encompasses at least one of the improved features summarized above and disclosed more fully hereinafter.
These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.